Some completion procedures require a series of plugs for sequential operations in one zone while isolating already treated zones. At the end of the operation for all the zones, the plugs are typically removed. One fast way to remove such plugs is to drill them out. To facilitate drilling out the plugs are made from materials that can be drilled out fast such as composites. The design challenges are to build a barrier that will hold large pressure differentials while being amenable to a fast drilling out. Along those lines manufacturers have made more component parts from composite materials but the extrusion rings that are disposed on opposed sides of the sealing element to contain the sealing element when in the radially extended and set position. These backup rings have been a stack of thin circular sheets that bend into an L shape when the seal element is compressed. These stacks of thin metal rings are difficult to mill out. Typical of such designs is US 2013/0112412.
What is needed and provided by the present invention is a backup ring system that can tolerate high degree of expansion and still be easy to drill out. The high degree of expansion can be made necessary if there is a constriction in the tubular string for any reason and the plug needs to get past the constriction and still be operative to be set at another location for holding anticipated differential pressures. The backup ring system presents a plurality of connected rings that have weak connections such that on setting using cones that ramp out slips and the backup rings the rings break into segments defining gaps between the segments in each ring. The segment gaps in one ring are offset from segment gaps in the adjacent ring to present an effective extrusion barrier while using preferably composite components for the rings. These and other features of the present invention will be more readily apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.